This invention relates generally to synchronous transfer mode (STM) call completions and, in particular, to the completion of calls which originate and terminate in an STM network but at least a portion of the call connection is completed using a broadband data network, for example an asynchronous transfer mode (ATM) network or an Internet Protocol (IP) network.
Multi-service broadband networks built using ATM or IP protocols are gaining acceptance as the preferred transport backbone for STM service providers because they permit the service providers to consolidate their voice and data traffic on a single multi-service facility. Consequently, the use or the desire to use ATM/IP networks as transport backbones for STM calls is rapidly increasing. As new facilities are added to ATM/IP networks for the admission of STM calls, a problem arises respecting address resolution to determine an appropriate broadband data destination node for servicing each call admission request.
Call setup and control in the public switched telephone network (PSTN) is generally effected using an out-of-band signaling network known as a common channel signaling network. Most of the North American PSTN is equipped to operate with a common channel signaling protocol called Signaling System 7 (SS7). ATM networks, for example, use a different signaling protocol in which signaling messages are transported through the network in cells like those used for carrying payload data. The signaling systems of the PSTN and ATM networks are therefore incompatible and STM calls cannot be transferred directly to or from an ATM network. Although it is possible to adapt an ATM network to operate under the control of a common channel signaling network, as taught in U.S. Pat. No. 5,568,475 entitled xe2x80x9cATM NETWORK ARCHITECTURE EMPLOYING A COMMON CHANNEL SIGNALING NETWORKxe2x80x9d, which issued on Oct. 22, 1996 to Doshi et al, it is less expensive and preferable to permit the ATM multi-service carrier network to operate autonomously with its native signaling system. This minimizes expense while enabling efficient use of ATM network resources. The same applies to the use of multi-service IP networks which currently run on a dynamic routing system for the purpose of data services, and one not adapted to support signaling.
In the STM network, time division multiplex switches are arranged in a hierarchy which minimizes address encoding and permits calls to be completed with a minimum of address resolution. A factor which contributes to the efficiency of broadband data networks is that such a switch hierarchy does not exist. While this lack of hierarchy contributes to network efficiency and versatility, it imposes a requirement for address resolution to enable STM calls to be transferred through the ATM network at an acceptable call setup rate. Likewise, an address resolution system is required to enable STM calls to be transferred through an IP network because IP does not support the PSTN numbering system.
There therefore exists a need for a method of address resolution to enable the transfer of STM calls through multiple domains in a broadband data network. There also exists a need for a messaging protocol for called number address resolution in a multiple domain control network adapted to control the transfer of STM calls between STM switches using a broadband data backbone.
It is an object of the invention to provide a method of address resolution for the transfer of STM calls through a broadband data network which enables automated data fill and maintenance of translation tables to enable address resolution.
It is a further object of the invention to provide a method of address resolution for the transfer of STM calls through multiple domains in a broadband data network in which a switched virtual circuit is set up from a destination node for a call in order to minimize call setup time.
It is yet a further object of the invention to provide a method of address resolution for the transfer of STM calls through multiple domains across a broadband data network in which each domain includes at least one voice gateway node having a control virtual circuit established with a peer voice gateway node in an adjacent domain.
It is a further object of the invention to provide a method in which voice gateway nodes maintain next-hop call resolution routing tables which enable call routing without requiring a complete address mapping table indicating the destination node to serve a dialled number.
It is yet another object of the invention to provide a method of address resolution for the transfer of STM calls through a broadband data network in which all nodes in a domain of the broadband data network maintain a complete map of dialled numbers served by nodes in the domain.
These and other objects of the invention are realized by a method of address resolution for the transfer of synchronous transfer mode (STM) calls through multiple domains across a broadband data network, comprising the steps of: checking a called number translation table at an edge node in the broadband data network which receives an admission request for the call to determine whether an address of a destination node to serve the called number is known; if the address is known, setting up an egress of the call from the broadband network; if the address is not known, formulating a query message at the edge node to determine the address of a destination node that serves the called number; and forwarding the query message to at least one predetermined node in the broadband data network to request a translation of the called number to determine the address of the destination node; and for a predefined number of hops, forwarding the query message to at least one other node if a node receiving the query does not possess information to enable the translation.
In accordance with a further aspect of the invention there is provided a messaging protocol for called number address resolution in a broadband data network adapted to transfer synchronous transfer mode (STM) calls between synchronous transfer mode (STM) switches, comprising: a message header portion that contains fixed length fields for mandatory information common to all messages; and a message content portion that contains a variable number of content objects, each content object including a content type indicator, a length indicator and content data.
The invention therefore provides a method of address resolution and a messaging protocol for address resolution which facilitates the transfer of STM calls through multiple domains in a broadband data network, such as an ATM or an IP network In accordance with the method, the voice edge nodes are preferably organized in domains which consist of a collection of edge nodes in the broadband data network that are equipped to accept STM call admission requests, each edge node being equipped with a voice interface control unit described in applicant""s U.S. Pat. No. 6,195,714, entitled SYSTEM FOR TRANSFERRING STM CALLS THROUGH ATM NETWORK BY CONVERTING THE STM CALLS TO ATM AND VICE VERSA AT THE EDGE NODES OF ATM NETWORK. The specification of that application is incorporated herein by reference in its entirety. The collection of edge nodes are logically fully meshed by control virtual circuits for call control and address resolution message forwarding if the broadband network is an ATM network.
In the description of the preferred embodiments of the invention which follows, reference is made principally to ATM networks, which are currently used for STM call transfer. It will be understood by those skilled in the art that the principles described may be applied with minimal revision to IP networks, as will be described below in more detail. Each domain includes at least one gateway switch. A gateway switch is a broadband edge node having a known path to at least one peer gateway in an adjacent domain. Gateway switches serve as voice call control paths between domains and are preferably enabled to maintain address resolution information respecting other domains in the broadband data network. This imposes a hierarchy on the voice edge nodes connected to the broadband data network, although the broadband data network is not aware of the hierarchy and not encumbered by it.
The methods and the messaging protocol in accordance with the invention therefore permit automatic maintenance of routing tables to enable address resolution for STM calls admitted to a broadband data network without imposing non-native signaling protocols on the broadband data network or integrating a common channel signaling network into the broadband data network. Thus, STM traffic can be rapidly and economically transferred to broadband data facilities with a minimum of preparation and consequently a minimum of expense.
In the case of an IP network connectionless service is used for call control and address resolution routing.